Calculating insulin on board for extended bolus being delivered by an insulin delivery device

ABSTRACT

A system and method may be used to calculate insulin on board (IOB) for an extended bolus being delivered by an insulin infusion pump. In general, the system and method calculates an extended bolus IOB value for the extended bolus, which takes into account the insulin currently on board from the extended bolus and the insulin scheduled to be delivered by the extended bolus over a subsequent time period equivalent to a duration of insulin action. The extended bolus IOB value may be used to calculate a suggested bolus.

TECHNICAL FIELD

The present invention relates to insulin delivery systems and methodsthat deliver insulin to a patient and more particularly, to a system andmethod for calculating insulin on board for an extended bolus beingdelivered by an insulin delivery device.

BACKGROUND INFORMATION

With advances in technology, medical devices are capable ofsignificantly improving the treatment and/or management of variousdiseases or illnesses. One such medical device is an insulin deliverysystem capable of delivering insulin to a diabetic individual andmanaging the delivery of insulin. One example of an insulin deliverysystem includes an insulin delivery device or infusion pump that issecured to the user to deliver the insulin and a wireless, hand-helddevice that communicates with the delivery device to control and manageinsulin delivery. The hand-held device may program the infusion pumpwith personalized insulin delivery instructions and monitor theoperation of the infusion pump, thereby facilitating the management ofdiabetes. The insulin infusion pump may deliver insulin according to adelivery program that provides different doses of insulin at differenttimes of day, for example, a basal program that provides different basalrates over different time segments. The insulin infusion pump may alsodeliver bolus doses of insulin, for example, to correct for high bloodglucose or in connection with an event, such as a meal, that is likelyto affect blood glucose. Extended bolus doses may be delivered, forexample, over an extended period of time to avoid a high initial dose ofinsulin and to allow extended insulin action.

Existing insulin delivery systems may calculate appropriate amounts ofinsulin to be delivered based on a number of factors. Insulin deliverysystems may calculate an appropriate bolus dose based on, for example, ablood glucose level and an expected carbohydrate intake. Another factorthat may be considered when determining an appropriate bolus dose isinsulin on board (IOB). Because insulin takes time to be processed inthe body, residual insulin often remains in the body for a period oftime after receiving the insulin and keeps working after thecarbohydrates have been processed. To avoid delivering a bolus dose thatwould result in too much insulin (e.g., insulin stacking), the IOB maybe subtracted from a bolus dose that would otherwise be appropriate(e.g., for a given blood glucose level and carbohydrate intake). Becauseinsulin is delivered over an extended period of time during an extendedbolus, factoring in the IOB during such extended boluses is moredifficult.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood byreading the following detailed description, taken together with thedrawings wherein:

FIG. 1 is a diagrammatic view of an insulin delivery system, consistentwith one embodiment of the present invention.

FIG. 2 is a diagrammatic view of an insulin delivery system includingone embodiment of a system for calculating insulin on board and forcalculating a suggested bolus.

FIG. 3 is a flow chart illustrating one method of calculating insulin onboard for an extended bolus, consistent with an embodiment of thepresent invention.

FIG. 4 is a flow chart illustrating one method of calculating asuggested bolus using an extended bolus IOB value, consistent with anembodiment of the present invention.

FIG. 5 is a graph illustrating one example of insulin on boardcalculated for an extended bolus using different methods.

FIG. 6 is a graph illustrating another example of insulin on boardcalculated for an extended bolus dose using different methods.

DETAILED DESCRIPTION

An insulin on board (IOB) calculation system and method, consistent withembodiments described herein, may be used to calculate insulin on boardfor an extended bolus being delivered by an insulin infusion pump. Ingeneral, the system and method calculates an extended bolus IOB valuefor the extended bolus, which takes into account the insulin currentlyon board from the extended bolus and the insulin scheduled to bedelivered by the extended bolus over a subsequent time period equivalentto a duration of insulin action. The extended bolus IOB value may beused to calculate a suggested bolus and/or to provide insulin on boardinformation to the user for other purposes.

As used herein, “insulin on board” generally refers to insulin that isin the body effectively lowering blood glucose. As described in greaterdetail below, “insulin on board” may include insulin that is currentlyin the body at a particular time and/or insulin that will be in the bodyduring a period of time in the future.

As used herein, “extended bolus” refers to an infusion of apredetermined amount of insulin that includes at least a portionextended over a period of time instead of being delivered immediately.In an embodiment, the period of time of an extended bolus may be atleast 30 minutes. An extended bolus may include a bolus in which aportion of the insulin is delivered immediately and a portion of theinsulin is delivered over the extended period of time. An extended bolusor the extended portion of an extended bolus is generally provided tocover carbohydrate intake (i.e., a meal bolus), although at least aportion of an extended bolus may also be provided to correct a highblood glucose level (i.e., a correction bolus). The duration of time ofan extended bolus may vary depending upon various factors such as thenature of the food for which the bolus is being taken (e.g., high fathigh protein foods may raise blood sugar for an extended time) and/orthe person receiving the insulin (e.g., the ability to digest).

As used herein, “duration of insulin action” refers to the amount oftime during which insulin effectively lowers blood glucose. Duration ofinsulin action may be specific to the person receiving the insulin andmay be a user-specified value. Currently available rapid/short actinginsulin, for example, may have a duration of insulin action betweenabout 3-5 hours. As used herein, a time period “substantially equal to”the duration of insulin action refers to a time period that is eitherthe same as the duration of insulin action or that varies from theduration of insulin action by some relatively small amount that is notlikely to have a significant impact on the user when calculating IOBvalues and/or suggested boluses as described herein.

As used herein, “suggested bolus” refers to a bolus that is determinedto be appropriate for a user at a particular time and may be based on anamount of insulin that will cover the anticipated increase in bloodglucose from a carbohydrate intake and/or an amount of insulin that willreduce a blood glucose level to within a target blood glucose range. Asuggested bolus may include meal bolus and correction bolus components.A “meal bolus” refers to a bolus that is based on an amount of insulinthat will cover a carbohydrate intake. A “meal bolus” is not limited toa meal per se and may be associated with any form of carbohydrateintake. A “correction bolus” refers to a bolus that is based on anamount of insulin that will reduce a blood glucose level to within atarget blood glucose range.

Referring to FIG. 1, an IOB calculation system and method, consistentwith embodiments of the present invention, may be implemented in aninsulin delivery system 100 used by a user or patient 102. Oneembodiment of the fluid delivery system 100 may include a hand-helddelivery management device 104 and an infusion pump 106 worn by thepatient 102. In the exemplary embodiments, the delivery managementdevice 104 communicates with the infusion pump 106, for example, over awireless communication link 108, to program and monitor the infusionpump 106 and to manage delivery of a fluid, such as insulin, to apatient according to a treatment regimen. One example of such amanagement device 104 and infusion pump 106 is the OmniPod® insulinmanagement system available from Insulet Corporation. The IOBcalculation system and method may also be used with a fluid deliverysystem in which the management device and the infusion pump areintegrated as a programmable infusion pump. Those skilled in the artwill recognize that the IOB calculation system and method, described ingreater detail below, may be used in any type of insulin delivery systemor fluid delivery system.

According to the exemplary embodiment, the delivery management device104 may include a fluid delivery control system 110 for controllingdelivery of the fluid, for example, by programming the infusion pump 106with personalized delivery instructions that specify certain doses atcertain times of day. The fluid delivery control system 110 may includehardware, software, firmware or any combination thereof to perform thefluid delivery control functions. The delivery management device 104 mayalso include user interface components 112, such as a visual display,audio devices, and electromechanical switches, for allowing a user toreceive and provide information. The delivery management device 104 mayfurther include transmitter and receiver components (not shown), such asa wireless transceiver, for communicating with the infusion pump 106using radio frequency or other wireless communication standards andprotocols. One example of the insulin delivery system, and particularlythe user interface, is disclosed in greater detail in U.S. patentapplication Ser. No. 10/827,582 filed on Apr. 19, 2004 (U.S. PatentApplication Publication No. 2005/0022274), which is commonly owned withthe present application and fully incorporated herein by reference.

According to the exemplary embodiment, the infusion pump 106 may includefluid delivery components (not shown), such as a dispenser assembly forcausing fluid from a fluid reservoir to flow through a flow pathassembly to a transcutaneous access tool (e.g., a needle) for infusionto a patient. The infusion pump 106 may also include one or more memoryunits and one or more processor units (not shown) that are capable ofstoring and executing the instructions provide by the deliverymanagement device 104. The infusion pump 106 may further include asystem clock (not shown) that keeps the time of day (referred to as theprogram time) to determine when certain programmed doses of fluid shouldbe delivered. The infusion pump 106 may also include transmitter andreceiver components (not shown), such as a wireless transceiver, forcommunicating with the delivery management device 104.

In general, the delivery management device 104 is used to remotelyinitialize and program the infusion pump 106 with a patient's customfluid delivery profile. The delivery management device 104 may set thesystem clock (or program time) of the infusion pump 106 to correspond tothe local time on the delivery management device 104. The fluid deliverycontrol system 110 may also generate or establish one or more fluiddelivery programs 120 to be transmitted to the infusion pump 106, forexample, over the wireless communication link 108. Fluid deliveryprograms may include, but are not limited to, basal programs, temporarybasal rates, and/or bolus doses. In a basal program, for example, thedifferent doses of fluid may be different basal rates of fluid deliveredover basal rate time segments. Bolus doses may include, for example,meal boluses and/or correction boluses. The infusion pump 106 mayprovide bolus doses immediately (i.e., immediate boluses) and/or over anextended period of time defined by the fluid delivery program (i.e.,extended boluses). The fluid delivery program 120 may includeinstructions that, when executed by the infusion pump 106, cause theinfusion pump 106 to provide the specified doses at the specified times.

The infusion pump 106 may operate according to the fluid deliveryprogram(s) 120 on the infusion pump 106 independently of the deliverymanagement device 104, for example, until the fluid delivery controlsystem 110 on the delivery management device 104 alters or stops thefluid delivery program and/or provides a new fluid delivery program. Thedelivery management device 104 may also be used to check the status ofthe infusion pump 106 and/or the active delivery program, to cause theinfusion pump 106 to deliver additional doses (e.g., temporary basalrates or bolus doses), to suspend delivery and/or to modify the fluiddelivery program(s).

The delivery management device 104 may also be used to determine asuggested bolus based on various factors including, without limitation,insulin on board (IOB), duration of insulin action,insulin-to-carbohydrate (I/C) ratios, insulin correction factors, bloodglucose levels and carbohydrate intake. When extended boluses arerunning, for example, the delivery management device 104 may calculatean extended bolus IOB value taking into consideration the actual insulinon board and insulin to be delivered in a subsequent time periodequivalent to the duration of insulin action.

As shown in FIG. 2, one embodiment of an IOB calculation system may beimplemented as software on a fluid delivery system 200. The fluiddelivery system 200 may include fluid delivery control system 210, userinterface 212 coupled to the fluid delivery control system 210, andinfusion pump 214 coupled to the fluid delivery control system 210. Inone embodiment, the fluid delivery control system 210 and user interface212 may be implemented on a hand-held delivery management device (e.g.,as shown in FIG. 1) separate from the infusion pump 206. The fluiddelivery control system 210, user interface 212 and the infusion pump214 may also be integrated into a single programmable pump device. Thefluid delivery control system 210 may include one or more memory units220 and one or more processing units 222 for storing and executing theIOB calculation software and other software such as suggested boluscalculation software.

The fluid delivery control system 210 may include IOB calculation code230 including a series of instructions that, when executed by theprocessing unit 222, embody all or part of the functionality describedherein with respect to the IOB calculation system and method. The fluiddelivery control system 210 may also include suggested bolus calculationcode 236 including a series of instructions that, when executed by theprocessing unit 222, embody all or part of the functionality describedherein with respect to calculating suggested bolus doses.

The fluid delivery control system 210 may also include fluid deliveryprogram data 232 and/or user data 234 used to calculate the insulin onboard and/or the suggested bolus. The fluid delivery program data 232may include data defining the specified delivery doses (e.g., bolusdoses) and the specified durations and/or times (e.g., duration of anextended bolus) of doses being delivered according to one or more fluiddelivery programs. In one example, the fluid delivery program data 232may include dose amounts for each of a plurality of time segments over a24 hour day (e.g., bolus amounts for half hour time segments). For anextended bolus, the fluid delivery program data 232 may also includedata representing an amount already delivered (i.e., a completedportion), an amount remaining to be delivered (i.e., a scheduledportion), a time elapsed and a time remaining. The user data 234 mayinclude data specific to the user such as duration of insulin action,blood glucose levels, insulin-to-carbohydrate (I/C) ratios, correctionfactors and carbohydrate intake amounts. The user data 234 may alsoinclude insulin delivery history data representing insulin delivered tothe user over a previous period of time (e.g., previous completedboluses) and calculated IOB values.

Those skilled in the art will recognize that the IOB calculationsoftware and suggested bolus calculation software may be created usingvarious formats and programming languages. Although the exemplaryembodiment is described and shown as one software implementation of theIOB calculation system and method, those skilled in the art willrecognize that alternative embodiments may be implemented using any typeof circuitry or logic, such as pre-programmed hardware elements or as acombination of hardware, software and/or firmware.

Referring to FIG. 3, one method of calculating insulin on board for anextended bolus that is currently running is shown and described. In oneembodiment, the extended bolus is a meal bolus that was initiated tocover an anticipated increase in blood glucose level as a result of acarbohydrate intake. The method includes determining 310 a duration ofinsulin action (DIA) value to be used in the IOB calculation. Theduration of insulin action may be determined, for example, by retrievinga stored DIA value or by receiving a DIA value input by the user.

The method includes determining 312 a completed IOB value representingan amount of insulin on board from a completed portion of the extendedbolus, which has been completed within a previous time periodsubstantially equal to the duration of insulin action. The completedportion of the extended bolus may be represented by a series ofimmediate bolus portions delivered at different times during theprevious time period. For an extended bolus of 6 units delivered over anextended period of 6 hours, for example, the extended bolus may berepresented by a series of twelve 0.5 unit immediate bolus portionsdelivered every ½ hour and the completed portion after 2 hours may berepresented as a series of four 0.5 unit immediate bolus portionsdelivered every ½ hour. The completed IOB value may thus be determinedby calculating IOB values for each of the immediate bolus portions atthe respective times and adding the calculated IOB values for the seriesof immediate bolus portions within the previous time period.

According to one example, each of the calculated IOB values for animmediate bolus portion of a completed portion of an extended bolus maybe calculated as follows:

IOB=(V×(1−T _(e)/DIA))   (1)

where V is the volume of the immediate bolus portion that was delivered,DIA is the duration of insulin action, and T_(e) is the elapsed timesince the immediate bolus portion was delivered. The IOB value for thecompleted portion of the extended bolus may then be calculated as thesum of the IOB values calculated for each of the immediate bolusportions as follows:

IOB_(c)=IOB₁+. . . IOB_(n)   (2)

where n is the number of immediate bolus portions in the completedportion of the extended bolus within the previous time periodsubstantially equal to the duration of insulin action. Other methods forcalculating the completed IOB value may also be used.

The method also includes determining 314 a scheduled IOB valuerepresenting an amount of insulin scheduled to be delivered during ascheduled portion of the extended bolus and within a subsequent timeperiod substantially equal to the duration of insulin action. Thescheduled IOB value may be calculated based on the extended bolusamount, the time remaining for the extended bolus, and the duration ofinsulin action. According to one example, the schedule IOB (IOB_(s)) iscalculated as follows:

IOB_(s) =V _(t)×(T _(s) /D)   (3)

where V_(t) is the total volume of the extended bolus, T_(s) is the timefor delivering the schedule portion of the extended bolus, and D is theduration of the extended bolus. The duration of the extended bolus maybe longer or shorter than the duration of insulin action. If the timeremaining in the extended bolus is more than the DIA, the time T_(s) fordelivering the scheduled portion is the DIA value. If the time remainingis less than the DIA, the time T_(s) for delivering the scheduledportion is time remaining in the extended bolus. Other methods forcalculating the scheduled IOB value may also be used.

The extended bolus IOB value may then be obtained 316 by adding thecompleted IOB value and the scheduled IOB value, for example, asfollows:

IOB_(e)=IOB_(c)+IOB_(s)   (4)

The extended bolus IOB value may then be stored, displayed to the userand/or used in other calculations such as a suggested bolus calculation.

FIG. 4 shows one method of calculating a suggested bolus, which takesinto account an extended bolus IOB value. The method may initiate 410 asuggested bolus calculation, for example, automatically or in responseto a user requesting a suggested bolus. To obtain insulin on boardinformation to be used in the suggested bolus calculation, the methodmay calculate IOB values for an extended bolus that is currently runningand/or for a previous bolus that was completed. After the IOBcalculation is initiated, for example, the method may determine 412 ifan extended bolus is running. If an extended bolus is running, thesystem may calculate 414 the insulin on board value(s) from thecurrently running extended bolus(es), for example, using the methoddescribed above.

The system may also determine 416 if any previous boluses have beendelivered within a previous time period substantially equal to theduration of insulin action. Such previous boluses may include extendedboluses that were completed during the previous time period and/orimmediate boluses (e.g., meal boluses or correction boluses) that weredelivered during the previous time period.

If any previous bolus had been delivered during the previous timeperiod, the method may then calculate 420 the insulin on board value(s)from those previous bolus(es). For a previous bolus that was animmediate bolus delivered during the previous time period, the previousbolus IOB value may be calculated as follows:

IOB=(V×(1−T _(e)/DIA)   (5)

where V is the volume delivered by the immediate bolus, DIA is theduration of insulin action, and T_(e) is the elapsed time since theimmediate bolus was delivered (e.g., measured from the time the boluswas completed).

For a previous bolus that was an extended bolus completed during theprevious time period, an IOB value may be calculated for the portion ofthe extended bolus that occurred during the previous time period. Asdescribed above, this completed portion of the extended bolus may berepresented by a series of immediate bolus portions delivered duringthat previous time period. This IOB value may thus be calculated bycalculating and summing the IOB values for the series of immediate bolusportions representing that portion of the extended bolus, for example,as described above.

The previous bolus IOB values may be calculated separately forcorrection boluses and meal bolus resulting in a separate correctionbolus IOB value and meal bolus IOB value. If multiple correction bolusesor meal boluses were given during the previous time period, thecorrection bolus IOB value or meal bolus IOB value may be calculated bysumming the IOB values for the correction boluses or meal bolusesrespectively. The calculation of insulin on board may also take intoaccount insulin on board from basal doses of insulin being delivered.

A suggested bolus may then be calculated 422 using the calculated IOBvalues. The suggested bolus may be calculated, for example, bycalculating a suggested correction bolus component and a suggested mealbolus component and by subtracting one or more of the calculated IOBvalues to determine an effective suggested correction bolus componentand an effective suggested meal bolus component.

A correction bolus may be calculated based on a current blood glucoselevel, a target blood glucose level or range, and an insulin correctionfactor. The target blood glucose level and correction factor may beretrieved from the user data stored in the system or received from userinput. The current blood glucose level may be obtained, for example, bytesting and inputting the test data into the system or by usingcontinuous glucose monitoring (CGM) integrated into the insulin deliverysystem.

According to one example, a correction bolus may be calculated asfollows:

CB=(CBG−TBG)/CF   (6)

where CBG is the current blood glucose level (e.g., in mg/dl), TBG is atarget blood glucose level (e.g., in mg/dl), and CF is CF is thecorrection factor. In some cases, the correction bolus may be determinedto be 0 if the current blood glucose level does not exceed a targetblood glucose correction threshold. In some cases, the correction bolusmay be calculated to be a negative number to provide a reversecorrection if the current blood glucose level is below a target bloodglucose level or range.

The effective suggested correction bolus may be calculated bysubtracting one or more of the calculated IOB values described above. Inone embodiment, the effective suggested correction bolus may becalculated by subtracting both correction IOB values and meal IOB valuesincluding extended bolus IOB values. The effective suggested correctionbolus may also be adjusted by a user.

A meal bolus may be calculated based on the carbohydrate intake and aninsulin-to-carbohydrate ratio. The insulin-to-carb ratio may be auser-specified data stored in the system or entered by the user. Thecarb intake value may be entered by the user or selected from a libraryof predetermined carb intake values. According to one example, a mealbolus may be calculated as follows:

MB=(C/IC)   (7)

where C is digestible carbohydrates from the carb intake and IC is theI/C ratio. Digestible carbohydrates may be determined by subtracting anamount (e.g., grams) of fiber from an amount (e.g., grams) ofcarbohydrates.

The effective suggested meal bolus may be calculated by subtracting oneor more calculated IOB values. In one embodiment, the effectivesuggested meal bolus may be calculated by subtracting a correction bolusIOB value but not a meal bolus IOB value. If the suggested bolusincludes both a meal bolus portion and a correction bolus portion, forexample, the meal bolus IOB value may be subtracted from the correctionbolus portion up to the point where the correction bolus would become 0,but the meal bolus IOB value would not be subtracted from the meal bolusportion.

If the suggested bolus includes only a meal bolus portion (i.e., a carbintake and the current blood glucose is in the target range or below thecorrection threshold), the suggested bolus may be calculated as follows:

SB=MB−IOB_(c)   (8)

where MB is the meal bolus and IOB_(c) is the total correction IOBvalue.

If the suggested bolus includes only a correction bolus portion (i.e.,the current blood glucose is above the target range or the correctionthreshold but no carb intake), the suggested bolus may be calculated asfollows:

SB=CB−IOB_(c)−IOB_(m)   (9)

where CB is the correction bolus, IOB_(c) is the total correction IOBvalue, and IOB_(m) is the total meal IOB value including both immediatemeal bolus IOB values and extended meal IOB values.

If the suggested bolus includes both a meal bolus portion and acorrection bolus portion, the suggested bolus may be calculated asfollows:

SB=RCB−IOB_(c)+MB   (10)

where RCB is a reduced correction bolus (i.e., the correction bolusreduced by the meal IOB value), IOB_(c) is the total correction IOBvalue, and MB is the meal bolus volume. The reduced correction bolus maybe calculated as follows:

RCB=CB−IOB_(m) if IOB_(m)<CB   (11)

RCB=0 if IOB_(m)>CB   (12)

where CB is the correction bolus and IOB_(m) is the total meal IOB valueincluding both immediate meal bolus IOB values and extended meal IOBvalues. Other methods for calculating a suggested bolus may also beused.

The IOB calculation system and method may also be used to calculate anextended bolus IOB value during an extended bolus dose for suggestingother doses of insulin. For example, the IOB calculation system andmethod may be used to calculate an extended bolus IOB for suggesting atemporary basal rate provided over a programmed period of time and/or asuspension of insulin for a period of time. The IOB from an extendedbolus may impact a temporary basal rate, the suspension of insulin, andan extended bolus as well as a correction bolus or a food bolus.

The extended bolus IOB value may also be calculated (e.g., together withother IOB values) to provide the user with insulin on board information.The insulin on board information may include the extended bolus IOBvalue, IOB values from other previous boluses (e.g., immediate meal andcorrection boluses), and/or a total IOB value. This insulin on boardinformation may be displayed or otherwise provided to the user. A usermay want to know insulin on board information if the user is about toengage in any activity affecting blood glucose levels, for example, ifthe user is about to exercise or eat a meal. If there is insulin onboard before exercise, the user may want to eat to avoid low bloodglucose levels. If there is insulin on board before eating, a user mayavoid an additional unnecessary infusion of insulin. A user may alsowant to know insulin on board information if the user is about tosuspend insulin delivery, for example, by disconnecting from an insulindelivery system.

The method of calculating an IOB as described herein may also be usedfor calculating IOB from a temporary basal rate and specifically fromincreased temporary basal rates. In this variation of the method, theamount of basal insulin above a “normal” basal rate may be used tocalculate the IOB by calculating an IOB value for the completed portionof the temporary basal rate and by calculating an IOB value for thescheduled portion of the temporary basal rate. Thus, the amount of basalinsulin above a “normal” basal rate may be considered to be a form of anextended bolus.

In other variations of the method described herein, a carbohydrateglycemic index may be used to indicate whether or not and how much theIOB should be considered with carbs that are known to absorb more slowly(e.g., a lower glycemic index). The carbohydrate glycemic index may becaptured, for example, via a user prompt at the time of carbconsumption.

FIGS. 5 and 6 illustrate examples of an extended bolus IOB calculation,consistent with embodiments of the present invention, compared to otherIOB calculations calculated using other techniques during an extendedbolus. According to both examples, the blood glucose level is 100 mg/dland is within a target range, the carbohydrate intake is 60 g, theextended bolus dose is 4 units, and the duration of insulin action is 3hours. The duration of the extension of the bolus is different in eachof the examples shown in FIGS. 5 and 6.

According to the example in FIG. 5, the duration of the extension of thebolus is 100% over 6 hours, which is greater than the duration ofinsulin action. The extended bolus IOB curve 510 represents the extendedbolus IOB value calculated according to the method described above. Asshown, at the start of the extended bolus, the extended bolus IOB valueis 2 units. At this time there is no completed portion and the scheduledIOB portion is calculated as 2 units to be delivered over the subsequent3 hour period. Because the duration of the extended bolus is longer thanthe duration of insulin action, the scheduled IOB portion of theextended bolus IOB value remains at 2 units until the time remaining isless than the duration of insulin action. The extended bolus IOB valueincreases as the completed IOB portion increases until the timeremaining is less than the duration of insulin action (i.e., after 3hours or 180 minutes). When the time remaining in the extended bolus isless than the duration of insulin action, the extended bolus IOB valuedecreases because the scheduled IOB portion decreases.

The extended bolus IOB value calculated consistent with embodiments ofthe present invention may have advantages over other approaches tocalculating the IOB during an extended bolus because such otherapproaches are either too aggressive or too conservative. The IOB curve512 shows a more conservative approach, which has much higher IOB valuesat the beginning of the extended bolus. This conservative approachconsiders all future extended bolus to be “on board.” Such an approachmay result in suggested bolus calculations that are too low at thebeginning of the extended bolus, which may cause insufficient insulindelivery and high blood glucose.

The IOB curves 514, 516 show more aggressive approaches, which have muchlower IOB values throughout most of the extended bolus. These approachesonly consider the insulin that is truly “on board” at the time. Suchapproaches may result in suggested bolus calculations that are too high,which may cause excessive insulin delivery and low blood glucose. Theextended bolus IOB values calculated consistent with embodiments of thepresent invention may thus prevent low blood glucose caused by asuggested bolus that is too aggressive and may prevent excessively highblood glucose caused by a suggested bolus that is too conservative.

According to the example in FIG. 6, the duration of the extension is100% over 2 hours, which is less than the duration of insulin action.The extended bolus IOB curve 610 represents the extended bolus IOB valuecalculated according to the method consistent with embodiments of thepresent invention. Because the duration of the extension is less thanthe duration of insulin action, the scheduled IOB portion (and theextended bolus IOB value) is calculated to be the full 4 units at thestart of the extended bolus. The extended bolus IOB value is thenreduced as a function of the scheduled IOB portion of the IOB valuebeing reduced. The IOB curves 612, 614, 616 again show other approachesto calculating the extended bolus IOB compared to the method describedherein. Accordingly, an extended bolus IOB calculation system andmethod, consistent with embodiments described herein, allows a morereliable determination of insulin on board and calculation of asuggested bolus.

Although exemplary embodiments described herein involve insulindelivery, the concepts of the extended bolus IOB calculation system andmethod described above may be applied to other types of drugs ormedicines that may be delivered as an extended bolus by an infusion pumpto treat or prevent a disease or illness. For such drugs the duration ofaction may be determined as the period of time in which the drug remainsactive in the body to treat a particular condition. If the duration ofaction for the particular drug or medicine can be determined, the systemand method described above may be used to calculate a bolus on board(BOB) value for that particular drug or medicine. The calculation of anextended bolus BOB value may take into account the amount of the drug ormedicine that is currently on board up to that point in time and theamount of drug or medicine scheduled to be delivered during a subsequenttime period substantially equal to the duration of action for thatparticular drug, for example, using the techniques described above.

Other types of drugs or medicines that can be delivered by an infusionpump include, but are not limited to, antibiotics, nutritional fluids,total parenteral nutrition or TPN, analgesics, morphine, hormones orhormonal drugs, gene therapy drugs, anticoagulants, analgesics,cardiovascular medications, AZT or chemotherapeutics. Other types ofmedical conditions that might be treated include, but are not limitedto, diabetes, cardiovascular disease, pain, chronic pain, cancer, AIDS,neurological diseases, Alzheimer's Disease, ALS, Hepatitis, Parkinson'sDisease or spasticity.

Consistent with one embodiment, a method is provided for calculatinginsulin on board (IOB) for an extended bolus being delivered by aninsulin infusion device. The method includes determining a completed IOBvalue representing an amount of insulin on board from a completedportion of the extended bolus that has been completed within a previoustime period substantially equal to a duration of insulin action;determining a scheduled IOB value representing an amount of insulinscheduled to be delivered during a scheduled portion of the extendedbolus within a subsequent time period substantially equal to theduration of insulin action; and adding the completed IOB value to thescheduled IOB value to produce an extended bolus IOB value.

Consistent with another embodiment, a method is provided for calculatinginsulin on board (IOB) for a user of an insulin infusion device. Themethod includes determining if the insulin infusion device is currentlydelivering an extended bolus; if the insulin infusion device iscurrently delivering at least one extended bolus, calculating at leastone extended bolus insulin on board (IOB) value that takes into accountan amount of insulin currently on board up to that point in time fromthe extended bolus and an amount of insulin scheduled to be deliveredfrom the extended bolus within a subsequent time period substantiallyequal to a duration of insulin action; determining if the insulininfusion device has delivered any previous bolus within a previous timeperiod substantially equal to the duration of insulin action; if theinsulin infusion device has delivered at least one previous bolus withinthe previous time period, calculating at least one previous insulin onboard (IOB) value for the at least one previous bolus; and adding the atleast one extended bolus IOB value and the at least one previous IOBvalue to produce a total IOB value.

Consistent with a further embodiment, a method is provided fordetermining a suggested bolus of insulin to be delivered by an insulininfusion device. The method includes: determining if the insulininfusion device is currently delivering an extended bolus; if theinsulin infusion device is currently delivering at least one extendedbolus, calculating at least one extended bolus insulin on board (IOB)value that takes into account an amount of insulin currently on board upto that point in time from the extended bolus and an amount of insulinscheduled to be delivered from the extended bolus within a subsequenttime period substantially equal to a duration of insulin action;determining if the insulin infusion device has delivered any previousbolus within a previous time period substantially equal to the durationof insulin action; if the insulin infusion device has delivered at leastone previous bolus within the previous time period, calculating at leastone previous insulin on board (IOB) value for the at least one previousbolus; and calculating a suggested bolus using at least one calculatedIOB value selected from the group consisting of the at least oneextended bolus IOB value and the at least one previous IOB value.

Consistent with yet another embodiment, a machine-readable mediumincludes contents that cause a processor to perform the method ofcalculating insulin on board for an extended bolus as described above.

Consistent with yet another embodiment, a method is provided forcalculating bolus includes: determining a completed BOB valuerepresenting an amount of the drug on board from a completed portion ofthe extended bolus that has been completed within a previous time periodsubstantially equal to a duration of action of the drug; determining ascheduled BOB value representing an amount of the drug scheduled to bedelivered during a scheduled portion of the extended bolus within asubsequent time period substantially equal to the duration of action;and adding the completed BOB value to the scheduled BOB value to producean extended bolus BOB value.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the exemplary embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention, which is not to be limited except by the following claims.

1. A method of calculating insulin on board (IOB) for an extended bolusbeing delivered by an insulin infusion device, the method comprising:determining a completed IOB value representing an amount of insulin onboard from a completed portion of the extended bolus that has beencompleted within a previous time period substantially equal to aduration of insulin action; determining a scheduled IOB valuerepresenting an amount of insulin scheduled to be delivered during ascheduled portion of the extended bolus within a subsequent time periodsubstantially equal to the duration of insulin action; and adding thecompleted IOB value to the scheduled IOB value to produce an extendedbolus IOB value.
 2. The method of claim 1 wherein the completed portionof the extended bolus is represented by a series of immediate bolusportions delivered at different times during the previous time period,and wherein determining the completed IOB value includes calculating IOBvalues for each of the series of immediate bolus portions at therespective times and adding the calculated IOB values for the series ofimmediate bolus portions.
 3. The method of claim 2 wherein thecalculated IOB values for each of the immediate bolus portions iscalculated according to the equation V×(1−T_(e)/DIA), wherein V is thevolume of the immediate bolus portion, DIA is the duration of insulinaction, and T_(e) is the elapsed time since the immediate bolus portionwas delivered.
 4. The method of claim 1 wherein the extended bolus is ameal bolus.
 5. A method of calculating insulin on board (IOB) for a userof an insulin infusion device, the method comprising: determining if theinsulin infusion device is currently delivering an extended bolus; ifthe insulin infusion device is currently delivering at least oneextended bolus, calculating at least one extended bolus insulin on board(IOB) value that takes into account an amount of insulin currently onboard up to that point in time from the extended bolus and an amount ofinsulin scheduled to be delivered from the extended bolus within asubsequent time period substantially equal to a duration of insulinaction; determining if the insulin infusion device has delivered anyprevious bolus within a previous time period substantially equal to theduration of insulin action; if the insulin infusion device has deliveredat least one previous bolus within the previous time period, calculatingat least one previous insulin on board (IOB) value for the at least oneprevious bolus; and adding the at least one extended bolus IOB value andthe at least one previous IOB value to produce a total IOB value.
 6. Themethod of claim 5 wherein calculating the at least one previous IOBvalue includes calculating a meal IOB value representing insulincurrently on board from a previous meal bolus given within the previoustime period and a correction IOB value representing insulin currently onboard from a previous correction bolus given within the previous timeperiod.
 7. The method of claim 5 wherein calculating the extended bolusIOB value comprises: determining a completed IOB value representing anamount of insulin on board from a completed portion of the extendedbolus that has been completed within a previous time periodsubstantially equal to a duration of insulin action; determining ascheduled IOB value representing an amount of insulin scheduled to bedelivered during a scheduled portion of the extended bolus within asubsequent time period substantially equal to the duration of insulinaction; and adding the completed IOB value to the scheduled IOB value toproduce the extended bolus IOB value.
 8. A method of determining asuggested bolus of insulin to be delivered by an insulin infusiondevice, the method comprising: determining if the insulin infusiondevice is currently delivering an extended bolus; if the insulininfusion device is currently delivering at least one extended bolus,calculating at least one extended bolus insulin on board (IOB) valuethat takes into account an amount of insulin currently on board up tothat point in time from the extended bolus and an amount of insulinscheduled to be delivered from the extended bolus within a subsequenttime period substantially equal to a duration of insulin action;determining if the insulin infusion device has delivered any previousbolus within a previous time period substantially equal to the durationof insulin action; if the insulin infusion device has delivered at leastone previous bolus within the previous time period, calculating at leastone previous insulin on board (IOB) value for the at least one previousbolus; and calculating a suggested bolus using at least one calculatedIOB value selected from the group consisting of the at least oneextended bolus IOB value and the at least one previous IOB value.
 9. Themethod of claim 8 wherein calculating the extended bolus IOB valuecomprises: determining a completed IOB value representing an amount ofinsulin on board from a completed portion of the extended bolus that hasbeen completed within a previous time period substantially equal to aduration of insulin action; determining a scheduled IOB valuerepresenting an amount of insulin scheduled to be delivered during ascheduled portion of the extended bolus within a subsequent time periodsubstantially equal to the duration of insulin action; and adding thecompleted IOB value to the scheduled IOB value to produce the extendedbolus IOB value.
 10. The method of claim 8 wherein calculating asuggested bolus dose includes: calculating a meal bolus portionrepresenting an amount of insulin to cover a carbohydrate intake;calculating a correction bolus portion representing an amount of insulinto correct blood glucose to within a target blood glucose range; andadding the carbohydrate bolus and the correction bolus and subtractingthe at least one calculated IOB value.
 11. The method of claim 8 whereincalculating the at least one previous IOB value includes calculating ameal IOB value representing insulin currently on board from a previousmeal bolus given within the previous time period and a correction IOBvalue representing insulin currently on board from a previous correctionbolus given within the previous time period.
 12. The method of claim 11wherein calculating a suggested bolus dose includes calculating a mealbolus representing an amount of insulin to cover a carbohydrate intakeand subtracting the correction IOB value.
 13. The method of claim 11wherein calculating a suggested bolus dose includes calculating acorrection bolus representing an amount of insulin to correct bloodglucose to within a target blood glucose range and subtracting the atleast one extended bolus IOB value, the meal IOB value, and thecorrection IOB value.
 14. The method of claim 10 wherein the suggestedbolus is an extended bolus.
 15. A machine-readable medium whose contentscause a processor to perform a method of calculating insulin on board(IOB) for an extended bolus delivered by an insulin infusion device, themethod comprising: determining a completed IOB value representing anamount of insulin on board from a completed portion of the extendedbolus that has been completed within a previous time periodsubstantially equal to a duration of insulin action; determining ascheduled IOB value representing an amount of insulin scheduled to bedelivered during a scheduled portion of the extended bolus within asubsequent time period substantially equal to the duration of insulinaction; and adding the completed IOB value to the scheduled IOB value toproduce an extended bolus IOB value.
 16. The machine-readable medium ofclaim 15 wherein the completed portion of the extended bolus isrepresented by a plurality of bolus portions delivered at differenttimes during the previous time period, and wherein determining thecompleted IOB value includes calculating IOB values for each of theplurality of bolus portions at the respective times and adding thecalculated IOB values for the plurality of bolus portions.
 17. Themachine-readable medium of claim 15 wherein each of the calculated IOBvalues is calculated according to the equation V×(1−T_(e)/DIA), whereinV is the volume of the bolus portion, DIA is the duration of insulinaction, and T_(e) is the elapsed time since the bolus portion wasdelivered.
 18. A method of calculating bolus on board (BOB) for anextended bolus being delivered by a drug delivery device, the methodcomprising: determining a completed BOB value representing an amount ofthe drug on board from a completed portion of the extended bolus thathas been completed within a previous time period substantially equal toa duration of action of the drug; determining a scheduled BOB valuerepresenting an amount of the drug scheduled to be delivered during ascheduled portion of the extended bolus within a subsequent time periodsubstantially equal to the duration of action; and adding the completedBOB value to the scheduled BOB value to produce an extended bolus BOBvalue.